1. Field
The present invention relates to a stator and a piezo ultrasonic motor including the same, and more particularly, to a stator and a piezo ultrasonic motor including the same, which can achieve stable driving characteristics and low manufacturing costs by reducing the number of elements and simplifying a structure.
2. Description of the Related Art
The recent rapid development of an information society has led to a demand for high-speed precision electronic and optical devices. Particularly, marketability of mobile application products for mobile phones is enhanced greatly every year to meet increasing interests of general consumers. Particularly, as pixels of a sensor increase in number, mobile phones provided with camera modules among those mobile application products are increasingly adopting digital camera functions such as automatic focusing and optical zooming, and thus competitive development thereof are being made for market occupancy.
A drive mechanism is used to drive such camera modules for mobile phones, which have high pixel resolution. Representative examples of the drive mechanism include a stepping motor, a voice coil motor, and a piezo ultrasonic motor. As for the piezo ultrasonic motor, it includes a piezoelectric body having a multilayer ceramic structure of piezoelectric ceramic sheets. The piezoelectric body causes simple vibration such as expansion and contraction when an electrical signal is applied thereto. The vibration is converted into a circular or linear movement by fractional contact between a stator and a rotor, so that the piezo ultrasonic motor can perform a motor function of generating a rotation force. As compared to an electromagnetic motor, the piezo ultrasonic motor has higher energy density, faster response time, and higher position accuracy. The piezo ultrasonic motor also has an off-power holding function, does not cause noise during operation, and is not affected by electromagnetic waves.
FIG. 1A is a perspective view of a related art stator, and FIG. 1B is a plan view of the related art stator. Referring to FIGS. 1A and 1B, a related art stator 1 includes a hollow cylindrical elastic body 2 formed of a ceramic material or a metal material, and plate-shaped first and second piezoelectric bodies 3 and 4 longitudinally provided on a first flat portion 2a and a second flat portion 2b of an outer surface of the elastic body 2, which have a phase difference of 90 degrees therebetween.
When an AC voltage, i.e., an electrical signal, is applied to the first and second piezoelectric bodies 3 and 4 through an external electrode (not shown) formed thereon, the first and second piezoelectric bodies 3 and 4 contract or expand in a longitudinal direction, thereby causing the elastic body 2 having a fixed length to relatively bend perpendicularly to the longitudinal direction. Thus, in the case of a bottom end of the elastic body 2 is fixed, a top end, which is free end, is displaced in a y-direction by the first piezoelectric body 3 and in an x-direction by the second piezoelectric body 4.
In this case, as AC voltages having different phases are respectively applied to the first and second piezoelectric bodies 3 and 4 as electrical signals, the top end of the elastic body 2 bends in the x-direction and in the y-direction, varying in its bending degree according to the AC voltage strength. Accordingly, a rotor (not shown) disposed in a central hole 5 of the elastic body 2 is rotated by contact between the rotor and the stator 2.
However, since the related art stator 1 needs to be manufactured through a high precision process, the manufacturing cost of the related art piezo ultrasonic motor increases. In detail, the first and second flat portions 2a and 2b on which the first and second dielectric bodies 3 and 4 are respectively mounted must be precisely formed so as to have a phase difference of 90 degrees therebetween. Then, the first and second piezoelectric bodies 3 and 4 must be precisely bonded on the first and second flat portions 2a and 2b. Thus, the manufacturing costs increase because of high precision processes required for the precise processing of the first and second flat portions 2a and 2b at the outer surface of the elastic body 2, and the precise bonding of the first and second piezoelectric bodies 3 and 4.
Also, a number of elements are used to constitute the stator 1, and thus the manufacturing cost of the piezo ultrasonic motors also increases.